Improve lighting

- No specular on surfaces facing away from the light source
- Transform the light direction to view space to ensure that all
  lighting calculations happen in a consistent coordinate space.
- Other lighting tweaks

glium_platform/src/render/basic.rs

@@ -59,7 +59,11 @@ impl RenderingSystem for BasicMeshRenderingSystem {
         };
 
         // Use HDR-derived environment light direction if provided, otherwise default to downward
-        let light_dir: Vec3 = if ctx.env_light_dir.length_squared() > 0.0 { ctx.env_light_dir.normalize() } else { Vec3::new(0.0, -1.0, 0.0) };
+        let light_dir_world: Vec3 = if ctx.env_light_dir.length_squared() > 0.0 { ctx.env_light_dir.normalize() } else { Vec3::new(0.0, -1.0, 0.0) };
+
+        // Transform light direction to view space (normals/positions are in view space)
+        let view_mat3 = glam::Mat3::from_mat4(cam.view());
+        let light_dir_view = (view_mat3 * light_dir_world).normalize();
 
         let asset_manager = ctx.asset_manager.borrow();
 
@@ -90,7 +94,7 @@ impl RenderingSystem for BasicMeshRenderingSystem {
                 model:      tr.matrix().to_cols_array_2d(),
                 view:       cam.view().to_cols_array_2d(),
                 projection: cam.projection().to_cols_array_2d(),
-                u_light:    [light_dir.x, light_dir.y, light_dir.z],
+                u_light:    [light_dir_view.x, light_dir_view.y, light_dir_view.z],
                 tex:        sampler,
                 color:      [c[0], c[1], c[2]],
                 uv_offset:  [mat.uv_offset.x, mat.uv_offset.y],

glium_platform/src/render/skybox.rs

@@ -119,7 +119,7 @@ impl RenderingSystem for SkyboxRenderingSystem {
 
 		// Load EXR from assets/exr
 		let manifest_dir = env!("CARGO_MANIFEST_DIR");
-		let path = std::path::Path::new(manifest_dir).join("../assets/exr/qwantani_sunset_puresky_2k.exr");
+		let path = std::path::Path::new(manifest_dir).join("../assets/exr/citrus_orchard_road_puresky_4k.exr");
 		let (equirect_srgb, light_dir) = Self::load_hdr_equirect_and_analyze(display, &path);
 		Self { program, quad_vb, quad_ib, equirect_srgb, light_dir }
 	}